Linear solar energy collector system and solar power generator system

ABSTRACT

A linear solar energy collector system includes reflective lines arranged in parallel in a south-north direction, heliostats mounted on the reflective lines, respectively, each comprised of mirror segments to reflect solar radiation, a light receiving line set above the reflective lines in a east-west direction, a receiver mounted on the light receiving line, to receive light reflected from the heliostats and collect heat from the light, and an angular adjuster to adjust angles of the mirror segments individually to irradiate a same light receiving area on the receiver with the reflected light from east-west neighboring reflective lines and thereby adjust a concentration ratio.

CROSS REFERENCE TO RELATED APPLICATION

The present application is based on and claims priority from Japanese Patent Application No. 2012-68606, filed on Mar. 26, 2012 and No. 2012-247211, filed on Nov. 9, 2012, the disclosure of which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present invention relates to a linear solar energy collector system formed of reflective lines for solar radiation arranged in parallel and a solar power generator system incorporating the same.

BACKGROUND ART

As such a related art linear solar energy collector system, a linear Fresnel reflector system is well known.

FIG. 23A is a perspective view of an example of a related art linear Fresnel reflector and FIG. 23B is a view of the same seen from one end of a light receiving line, as disclosed in Solar 2004: Life, the Universe and Renewables “Steam-circuit Model for the compact Linear Fresnel Reflector Prototype” and U.S. Patent Application Publication No. US2009/0056703 (Reference 1), for example.

As shown in the drawings, the related art reflector comprises reflective lines L1, L2, . . . arranged in parallel on the ground and light receiving lines G1, G2, . . . provided at a certain cycle astride the columns of the reflective lines in parallel to the reflective lines. On each of the reflective lines L1, L2, . . . , a large number of rectangular mirror plates H as heliostats are disposed and on each of the light receiving lines G1, G2, . . . receivers as a heat collector are provided in parallel with a certain spacing.

The rotation angles of the mirror plates H are individually controlled around a rotation axis to reflect incident solar radiation to respective neighboring receivers R. The heat of the reflected light at the receivers R is transformed into high-temperature water vapor via a heat medium. The reflective lines L1, L2, . . . and the receivers R are both arranged in parallel in a south-north direction. The angle of the reflective line L1, L2, . . . is adjusted in an east-west direction so that the mirror plates H thereon can track solar motion and allow the reflected light to be always collected in the vicinity of the receivers R.

The solar energy collector is used in a solar power generator system. There are commercial power plants in operation such as a parabolic trough solar generator system or a central tower solar generator system. The parabolic trough solar power generator system uses a gutter-like parabolic mirror having pipes on the focal position to collect solar radiation and heat fluids as oil flowing in the pipes, and produce thermal energy, thereby generating electric power. The central tower solar power generator system uses a plane mirror with a solar tracking device and a collector of a tower at the center to concentrate solar radiation and retrieve heat from fluids flowing in the top of the tower, thereby generating electric power.

The parabolic trough type generates power at relatively low costs but cannot operate efficiently due to a low temperature of heated fluids. The central tower type can generate high-temperature fluids but is not cost efficient since it requires accurate energy concentration.

Meanwhile, the linear Fresnel reflector is a simple structure with a relatively low rigidity and high land-use efficiency and insusceptible to wind, compared with the parabolic trough type or central tower type. It is one of the solar power generator systems which receive largest attention as a commercial plant because it can realize low-cost generation.

However, such a linear Fresnel type has a drawback that it suffers a large optical loss in solar radiation and faces difficulty in achieving high collection efficiency for the following reasons.

The optical loss of solar radiation is caused by cosine loss where solar rays are incident on a mirror plate not directly facing the sun, blocking where solar rays reflected by one mirror plate is shaded by another mirror plate, or shadowing where solar rays to be incident on one mirror plate is shaded by another mirror plate.

FIG. 24 shows the occurrence of cosine loss and blocking. Shadowing is not shown in the drawing and it often occurs especially when solar radiation is obliquely incident on the mirrors.

The optical loss is likely to be large if the mirror plates H are inclined at a large angle relative to the ground surface or the rotation angle of the mirror plates H are largely changed for tracking solar altitude. In FIG. 24 with the receivers R of a linear Fresnel type south-north oriented, for example, the mirror plates H on the reflective lines are inclined in an east-west direction to reflect solar rays to irradiate one of the receivers R. Because of this, the further from the receivers R the reflective lines are, the more inclined relative to the ground surface the mirror plates on the reflective lines are, so that the optical loss due to cosine loss and blocking increases.

Besides, to track solar trajectory from morning to evening, the angle of the mirror plates H has to be adjusted at about ±45 degrees or more. Therefore, at low solar altitude as in the morning and evening, a diurnal change amount of the collected solar energy is particularly increased by the optical loss due to the cosine loss and blocking. The temperature of acquired water vapor remains at 400 to 500 degrees C. at most and cannot reach 600 degrees C. or more.

From another point of view, a large number of mirror plates can be arranged on the reflective lines in the east-west direction to enlarge the area in which the mirrors are installed. However, the mirror plates far from the receivers cannot achieve a high thermal collection efficiency because of an increased optical loss. Moreover, the number of mirror plates from which a single receiver can receive reflected rays is limited so that with use of a large number of mirror plates over a large area, a light receiving line has to be provided for each group of mirror plates and the receiver R is needed for each light receiving line, to collect the heat of reflected rays received at each receiver. For these reasons, the temperature that the related art linear. Fresnel reflector can attain is limited to about 500 degrees C.

U.S. Patent Application Publication No. 2010/0012112 (Reference 2) discloses a linear Fresnel reflector in which the reflective lines and receivers are arrayed so that their lengths are parallel to the east-west direction, aiming for reducing the optical loss, as shown in FIG. 25. This reflector is configured that the mirror plates H on the reflective lines L1 μL2, . . . are not rotated in the east-west direction relative to solar trajectory but rotated only in the south-north direction to guide the reflected rays to the receivers.

With this reflector, the south-north rotation angle of the mirrors is very small as several degrees or less per day and about ±15 degrees per year, so that the optical loss can be reduced greatly. By arranging a large number of mirror plates in the south-north direction to increase the mirror area, the total amount of collected energy by the receivers can be increased.

However, there is a drawback that the reflector in Reference 2 cannot adjust the east-west mirror angle. This causes a problem that during a low solar altitude in the morning and the evening, the amount of collected energy per day is largely varied since the linear collecting areas of the mirror plates H are largely shifted from the surfaces of the receivers.

Moreover, in either of the reflectors in References 1 and 2 the solar rays irradiate the receivers linearly, almost uniformly due to the parallel arrangement of the reflective lines and the receivers. Re-radiation largely occurs in such irradiation areas at a high temperature about 600 degrees C., which likely decreases the amount of thermal energy absorbed into a heat medium.

Further, the reflector in Reference 1 faces problems that the exothermic temperature thereof remains only at 500 degrees C. because of the optical loss on the mirror plates, it suffers a large variation in collected energy amount per day, and even by use of a large number of mirror plates over a large area, thermal collection efficiency cannot be increased sufficiently because the further from the receivers the mirror plates, the larger the optical loss.

DISCLOSURE OF THE INVENTION

The present invention aims to provide a linear solar energy collector system which can reduce a variation in the amount of collected thermal energy relative to a diurnal change in solar altitude, decrease the optical loss, and improve heating efficiency.

According to one embodiment, a linear solar energy collector system includes reflective lines arranged in parallel in a south-north direction, heliostats mounted on the reflective lines, respectively, each comprised of mirror segments to reflect solar radiation, a light receiving line set above the reflective lines in a east-west direction, a receiver mounted on the light receiving line, to receive light reflected from the heliostats and collect heat from the light, and an angular adjuster to adjust angles of the mirror segments individually to irradiate a same light receiving area on the receiver with the reflected light from east-west neighboring reflective lines and thereby adjust a concentration ratio.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, embodiments, and advantages of the present invention will become apparent from the following detailed description with reference to the accompanying drawings:

FIG. 1 shows the basic structure of a linear solar energy collector system according to one embodiment;

FIG. 2 schematically shows the structure of mirror segments in FIG. 1;

FIG. 3 shows the rotation angle adjustment of the mirror segments in south-north and east-west orientations in FIG. 1;

FIG. 4 is a cross section view of a receiver in FIG. 1;

FIGS. 5A to 5C show the irradiated areas on light receiving lines in FIG. 1;

FIG. 6 shows an example of the arrangement of the mirror segments in FIG. 1;

FIGS. 7A to 7C show an example of structure model of the linear solar energy collector system in FIG. 1;

FIG. 8 is a top view of another example of structure model of the linear solar energy collector system in FIG. 1;

FIGS. 9A to 9C show a structure model of Reference 1;

FIGS. 10A to 10C show a structure model of Reference 2;

FIG. 11 is a graph showing the results of simulation of collecting heat using the structure models of the linear solar energy collector system in FIGS. 7A to 10C;

FIG. 12 shows an example of solar power generator system using the linear solar energy collector system in FIG. 1;

FIGS. 13A, 13B show a structure model of a linear solar energy collector system according to a first embodiment;

FIGS. 14A, 14B show a structure model of a linear solar energy collector system according to a second embodiment;

FIGS. 15A, 15B show a structure model of a linear solar energy collector system according to a third embodiment;

FIG. 16 is a side view of a structure model of a linear solar energy collector system according to a fourth embodiment;

FIGS. 17A to 17C show a structure model of a linear solar energy collector system according to a fifth embodiment;

FIG. 18 shows the essential part of the receiver in FIG. 17;

FIG. 19 shows a front view of a structure model of a linear solar energy collector system according to a sixth embodiment;

FIGS. 20A, 20B show a structure model of a linear solar energy collector system according to a seventh embodiment;

FIGS. 21A, 21B show a structure model of a linear solar energy collector system according to an eighth embodiment;

FIGS. 22A, 22B show a structure model of a linear solar energy collector system according to a ninth embodiment;

FIGS. 23A, 23B show an example of a related art linear Fresnel reflector disclosed in Reference 1;

FIG. 24 shows the effects of cosine loss and blocking; and

FIG. 25 shows another example of a related art linear Fresnel reflector disclosed in Reference 2.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

First, the basic structure of a linear solar energy collector system according to one embodiment is described. FIG. 1 shows an example of the arrangement of heliostats and receivers.

In the drawing this linear solar energy collector system is a linear Fresnel reflector comprising a group of reflective lines L1 to L8 and a light receiving line G. The reflective lines L1 to L8 are arranged in parallel in a thermal receiving zone Z on the ground in south-north orientation and heliostats 1 are mounted on the reflective lines L1 to L8. This collector system includes 8 reflective lines by way of example, however, the number of reflective lines should not be limited to 8, and can be set to an arbitrary number.

Solar radiation is incident on the elements on the reflective lines L1 to L8 and reflected thereby. Then, the mirror surfaces of the heliostats 1 on the reflective line L1 to L8 are adjusted in angle to reflect the solar radiation to the light receiving line G.

The light receiving line G is at a certain position above the center of the columns of the reflective lines L1 to L8 and extends in east-west direction or direction orthogonal to the reflective lines L1 to L8. A receiver 2 is installed on the light receiving line G and configured to receive the reflected light of solar radiation from the heliostats 1 and collect energy therefrom. With use of heliostats in size of 1 m by 2 m, the receiver is placed at a height of about 20 m.

The reflective lines L1 to L8 need to be accurately oriented south-north on the ground, however, a small shift in the arrangement from the south-north orientation is permissible as long as the receiver 2 on the light receiving line G can effectively receive the reflected light of the solar radiation incident on the heliostats 1. Likewise, a small shift in the position of the light receiving line from east-west orientation is permissible as long as the receiver 2 on the light receiving line G can effectively receive the reflected light of the solar radiation.

FIG. 2 schematically shows the structure of mirror segments arranged on the light receiving line in FIG. 1. Here, the structure of the heliostat 1 on the reflective line L1 is exemplified.

In FIG. 2 mirror segments 1 a, 1 b, 1 c, . . . as the heliostat 1 are disposed on the reflective line L1 in a certain area on the ground in row direction or south-north direction. Likewise, mirror segments are disposed on the reflective lines L2, L3, . . . along the row. The mirror segments 1 a, 1 b, 1 c . . . are thus arranged in a thermal receiving zone Z along the row.

FIG. 3 shows how to adjust the rotation angle of each mirror segment in the south-north and east-west directions.

In FIG. 3 the mirror segments 1 a, 1 b, 1 c, . . . in each column are mounted commonly on a main rotational shaft X extending in the south-north or row direction. The rotation of the main rotational shaft X is controlled by a column driver 3 in the east-west direction to adjust the rotation angle of the mirror segments 1 a, 1 b, 1 c.

Meanwhile, the mirror segments 1 a, 1 b, 1 c, . . . in each row are individually mounted on shafts Y1, Y2, Y3, . . . in orientation (east-west) orthogonal to the light receiving line G. The rotation thereof is individually controlled in the south-north orientation by row drivers 4 a, 4 b, 4 c, . . . placed on the shafts Y1, Y2, Y3, . . . to adjust the rotation angle of the mirror segments 1 a, 1 b, 1 c, . . . .

The rotation angle of the other heliostats 1 on the reflective lines L2, L3, . . . is also adjusted as above.

The mirror segments 1 a, 1 b, 1 c, . . . are each set to a standard module in south-north length of 1.0 m and lateral or east-west length of 2.0 m, for example. FIG. 1 shows one example of two units of five mirror segments 1 a to 1 e arranged in tandem in FIG. 2 on both sides of each reflective line. The number of mirror segments of one unit and the number of units on each reflective line should not limited to these numbers.

Further, the lengths of the north side and south side of each reflective line from the light receiving line do not need to be the same. In the northern hemisphere solar trajectory passes on the south side of the light receiving line, so that with this collector system installed in the northern hemisphere, the north-side length of the reflective line should be longer than the south-side to secure a wider mirror area on the north side to thereby improve thermal collection efficiency. Oppositely, to install the collector system in the southern hemisphere, the south-side length of the reflective line should be longer than the north-side to increase thermal collection efficiency.

In a dedicated area in which the reflective lines are installed, the south-north length along the row can be longer than the east-west length along the column. As described above, the receiver is placed in the east-west direction and the mirror segments are adjusted in angle to irradiate the light receiving line. Therefore, extending the reflective lines longer along the rows makes it possible to reduce the optical loss from that of a related art linear Fresnel reflector. Thus, with the mirror segments expansive in south-north orientation, the collector system can obtain a large amount of thermal energy with less optical loss. Also, the east-west length of the receiver can be shorter than that of a related art linear Fresnel reflector, leading to reducing thermal loss due to re-radiation of absorbed heat.

FIG. 4 is a cross section view of the receiver in FIG. 1. The receiver 2 comprises six parallel heat collecting pipes 6 as stainless pipes filled with a heat medium such as air or steam, placed over and astride all the columns of the heliostats or the reflective lines L1 to L8 and connected at one end to a heat source 5 in FIG. 1. The heat collecting pipes 6 are configured to receive light reflected from the heliostats 1, collect heat from a heated heat medium with the reflected light, and supply it to the heat source 5.

Further, the top of the heat collecting pipes 6 are covered with a thermal insulated wall 7 and an endothermic net 8 with a cavity window function is provided below the heat collecting pipes 6. The thermal insulated wall 7 has an arc-like cross section, encloses the heat collecting pipe arranged in parallel, and is covered at the bottom with the endothermic net 8. Both ends thereof project from the edges of the endothermic net 8 to substantially reduce convective thermal loss by ascending air currents inside the thermal insulated wall 7.

The endothermic net 8 is a stainless mesh with a curb or honey comb structure, to allow the reflected light from the heliostats to transmit therethrough and reach inside but not to allow irradiated light thereof to emit outside.

FIGS. 5A to 5C show the irradiations areas on the light receiving line in FIG. 1. Irradiation areas and non-irradiation areas are alternatively arranged with a certain spacing over the entire length of each heat collecting pipe 6 of the receiver 2. It is preferable to irradiate only the irradiation areas with the reflected light from the mirror segments 1 a, 1 b, . . . on the reflective lines, to thereby increase heat transfer efficiency to fluids in the heat collecting pipes.

FIG. 5A shows an example where five irradiation areas F1 to F5 are set over the total length P1 of the heat collecting pipe 6. Non-irradiation areas d in a certain length are disposed between the irradiation areas F1 to F5, and the irradiation areas F1 to F5 are separately arranged almost equally on the length P1 of the heat collecting pipe 6.

The irradiation areas F1 to F5 are irradiated with the reflected light by the mirror segments 1 a, 1 b, . . . to heat a heat medium in the heat collecting pipe 6. The heated heat medium is emitted from the irradiation area F5 to the heat source 5 in FIG. 1. Further, with the non-irradiation areas d thermally insulated, thermal radiation from these areas to outside is preventable so that the fluid inside the heat collecting pipe 6 can be heated to a higher temperature and emitted to the heat source 5.

FIG. 5B is a graph showing a fluid temperature distribution T1 relative to the heat collecting pipe in the length P1 having thermally insulated non-irradiation areas d. Another fluid temperature distribution T2 is of the heat collecting pipe without the non-irradiation areas when the reflected light collectively irradiates a specific area, as shown in FIG. 5C for comparison. It is apparent from the graph that T1>T2.

Thus, by disposing the non-irradiation areas d at both ends of each of the irradiation areas F1 to F5, not only the direct heat transfer from the irradiation areas F1 to F5 to the fluid via the non-irradiation areas but also that from the non-irradiation areas d to the fluid occur, to increase the length of period for which the fluid contacts the highly heated heat collecting pipe 6 and increase the amount of heat transfer from the heat collecting pipe to the fluid. Accordingly, higher-temperature fluid can be supplied to the heat source 5. Note that the lengths of the irradiation areas F1 to F5 and non-irradiation areas 5 should not be limited and the irradiation areas can be equally or unequally set on the total length P1 of the heat collecting pipe 6 freely.

In FIG. 1 the rotation angle of the mirror segments 1 a, 1 b, . . . on the reflective lines L1 to L8 are controlled in unit of a column in the east-west direction and individually in the south-north direction, to directly receive solar radiation and project it upward to the receiver 2.

The reflected light by the mirror segments 1 a, 1 b, . . . in each row and each column transmits through the space surrounded by the thermal insulated wall 7 via the endothermic net 8 and heats the heat medium in the heat collecting pipes 6. The heat medium is repeatedly heated to a high temperature by the reflected light transmitting through the heat collecting pipes. The heated heat medium is sent to the heat source 5 to use for generating high-temperature steam for steam turbine generation or for being processed to a chemical fuel by endothermic chemical reaction.

In the above-described linear solar energy collector system the spacing of the mirror segments on the reflective lines is constant irrespective of the magnitude of a distance to the receiver 2, by way of example.

As the distance from the receiver 2 to the mirror segments increases, the optical loss between the neighboring mirror segments increases by blocking. In order to prevent this, it is preferable to set different spacings between the mirror segments along the columns so that the further from the light receiving line the mirror segments are, the wider the spacing between them is.

As the distance from the light receiving line increases, the mirror segments are more affected by blocking. It is preferable to secure a space between the mirror segments on the south and north sides of the light receiving line G by changing the spacings. Alternatively, the mirror segments are divided into several zones from the position closest to the light receiving line G and the number of mirror segment in each zone can be changed.

As described above, the linear solar energy collector system in FIG. 1 comprises the receiver 2 on the east-west light receiving line G and adjust the angle of the mirror segments 1 a, 1 b, . . . on the reflective lines to irradiate the light receiving line G with the solar radiation reflected by the mirror segments. Because of this, the amount of the south-north angular adjustment of the mirror segments can be reduced to less than several degrees per day or several ten degrees per year which are about a half of the inclination at 23.4 degrees of the axis of the earth. The amount of optical loss along with a variation in the mirror angle can be decreased to a very small value.

Further, for the east-west angular adjustment of the mirror segments 1 a, 1 b, . . . , the solar radiation has only to be collected along the light receiving line so that the mirror angle relative to the incident solar radiation during culmination is smaller than that in related art. Because of this, the cosine loss and a variation in the optical loss relative to a change in a diurnal solar altitude can be decreased. Accordingly, a variation in the diurnal amount of collected energy can be reduced to a small value.

Next, the specific basic structure of the linear solar energy collector system according to one embodiment is described in detail. FIG. 6 shows an example of the arrangement of the mirror segments, in which the length of the reflective line is set to 210 m and the light receiving line G is placed 20 m above the height of the center thereof on which the receiver 2 is mounted. Moreover, a half of the reflective line of 105 m on both sides of the light receiving line G are equally divided into three, 35 m zones, D1, D2, D3 from the position closest to the light receiving line G. The number of mirror segments in zone D1 is 34, in zone D2 is 30, and in zone D3 is 26. The width of the receiver is 0.5 m. When receiving solar radiation, the amount of heat collected at the receiver is 400 kW/m² at insolation intensity of 0.8 kW/m².

70 reflective lines are arranged and 20 pipes are placed inside the receiver. Air gas at a room temperature and 10 atm is injected into one ends of the pipes. Through the 70 reflective lines, at current velocity of 2.5 m²/sec the air temperature is heated to about 700 degrees C. at the exit of the receiver. The collected energy of 400 kW/m² at the input of the receiver is five to ten times larger amount of energy than the related art linear solar energy collector system. The total collected power of the 70 reflective lines is 25 MW.

Next, the simulation results of structure models of the linear solar energy collector system in FIG. 1 and the related art, referring to FIG. 7A to 10C.

FIGS. 7A to 7C are a top view, a front view (from the east) and a south-side view of the structure model of the linear solar energy collector system in FIG. 1. FIG. 8 is a top view of another example. FIGS. 9A to 9C are a top view, a front view, and a side view of the structure model of Reference 1 while FIGS. 10A to 10C are the same of Reference 2.

In the structure model in FIGS. 7A to 7C (first example) the 8 reflective lines L1 to L8 are arranged in south-north orientation and the light receiving line G is disposed above them in east-west orientation to sterically cross the reflective lines L1 to L8. The number of mirror segments on the south and north sides of the light receiving line G is the same, four. The mirror face of each reflective line is adjusted in angle to reflect light to be incident vertically on the light receiving line G without a fail.

The structure model of FIG. 8 (second example) has almost the same structure as that in FIG. 7. A difference from that in FIG. 7 is in that the mirror segments are asymmetrically arranged relative to the light receiving line G, the number of mirror segments on the south side is 1 and that on the north side is 7, and the lengths of the area in which the reflective lines are arranged is longer along the rows (south-north) than along the columns (east-west). As in FIG. 7, the mirror face of each reflective line is adjusted in angle to reflect light to be incident vertically on the light receiving line G without a fail.

In the structure model of Reference 1 in FIGS. 9A to 9C, 8 reflective lines L1 to L8 are arranged in south-north orientation and a receiver R is disposed above the reflective lines in south-north orientation.

In the structure model of Reference 2 in FIGS. 10A to 10C, 8 reflective lines L1 to L8 are arranged in east-west orientation and a receiver R is disposed above the reflective lines in east-west orientation.

FIG. 11 shows the results of simulation of a diurnal variation in the amount of irradiation energy on the receiver of each structure model shown in FIG. 7A to FIG. 10C. The date, place and set conditions for the simulation are as follows.

Date: equinox day, Mar. 21, 2011

Place: Almeria, Spain (latitude: 36.84° north, longitude: 2.47° west)

Total area of the mirror segments: 64 m²

Length of receiver: 11 m

Height of receiver: 5 m from the ground

As shown in the graph, the structure model of Reference 1 exerts a relatively large amount of irradiation energy only in a short period of time during the morning and evening, however, the structure models in the first and second examples can exert a large amount of irradiation energy in total. By asymmetrically arranging the mirror segments 1 a, 1 b, . . . in line with latitude as in FIG. 8, for example, placing a larger number thereof on the north side if it is installed in the northern hemisphere or at a northern latitude as in the second example, the cosine loss of each mirror can be reduced, thereby increasing the irradiation energy amount.

Now, an example of a solar power generator system using the linear solar energy collector system in FIG. 1 as a repeater is described. It can heat pre-heated fluids to a higher temperature.

FIG. 12 shows an example of using four linear solar energy collector systems 10 a to 10 d in a tower solar energy collector system 11 as a relay. By this combination, the four collector systems 10 a to 10 d can separately heat preheated fluids at 300 degrees C. to 600 degrees C. and the tower solar energy collector system 11 further heats the fluids with collected heat to 800 degrees C.

Meanwhile, to collect heat and increase the temperature of fluids solely with the tower solar energy collector system 11 to realize a 100 MW plant, for example, the height of the tower has to be over 100 m and a heliostat field has to be extensive over several km. This requires an enormous amount of construction costs so that it is impossible to supply power at low costs.

In view of this, with use of the linear solar energy collector system in FIG. 1 as a backup heater, the fluids are pre-heated to 600 degrees C. lower than an intended temperature, for example, and then further heated to the intended temperature of about 800 degrees C., for example by another type collector system such as tower type as a main heater more suitable for high-temperature energy concentration than the linear solar energy collector system.

Thus, by using the linear solar energy collector system in FIG. 1 as a repeater to raise the temperature in two steps, a solar power generator system with less collected energy loss such as re-radiation can be provided in a reduced land area at reduced construction costs.

Next, first to fourth embodiments of the linear solar energy collector system are described. These embodiments aim to provide an improved linear solar energy collector system with an increased heating efficiency by increasing the concentration ratio of the light receiving line.

First, the concentration ratio is described. It is known that the collection efficiency nth of a solar power generator system to generate power using a heated heat medium is expressed by the following equation (1):

Hth=Qout/Qin

where Qout [W] is quantity of heat obtained by the heat medium in a receiver and Qin[W] is a solar radiation amount (refer to “New Solar Energy Use Handbook”, published by New Solar Energy Use Handbook Editorial Committee and Japan Solar Energy Society, May 1, 2010).

The quantity of heat Qout is derived from the energy obtained by the heat medium and thermal loss and expressed by the following equation (2):

Qout=Ib*Aa*ηopt*α−Ar*ε*σ*(Tr ⁴ −Ta ⁴)

where Ib is amount of solar radiation [W/m²], Aa is a mirror aperture area [m²], ηopt is collection efficiency, a is heat absorption rate of a receiver, Ar is receiver collection area, ε is heat radiation rate of a receiver surface, α is Stefan-Boltzmann constant [W/m²·K⁴], Tr is temperature of the receiver [K] and Ta is ambient temperature [K].

Also, the amount of solar radiation Qin is expressed by the following equation (3):

Qin=Ib*Aa

By substituting the equations (2), (3) into the equation (1), the following equation (4) is obtained:

ηth=ηopt*α−ε*σ*(Tr ⁴ −Ta ⁴)/(Ib*X)

where X (=Aa/Ar) is a concentration ratio.

From the equation (4), the maximum temperature Tr,max of the receiver is expressed by the following equation (5):

Tr,max⁴ =X*Ib*ηopt*α/(ε*α)+Ta ⁴

Thus, the concentration ratio X needs to be enlarged in order to heighten the temperature of the heat medium. In the present embodiment the angle of the mirror segments of the heliostats on the reflective lines are independently adjusted to adjust the light receiving positions on the receiver in east-west direction. Thereby, the concentration ratio of the receiver at an arbitrary east-west position can be freely set.

First Embodiment

FIG. 13A is a top view of a structure model of linear solar energy collector system according to a first embodiment while FIG. 13B is a side view of the same.

As shown in FIG. 13B, two east-west adjacent reflective lines each reflect light to a single irradiation area or light receiving position of the receiver 2, thereby increasing the concentration ratio X of the irradiation area double. This is equivalent to doubling the mirror aperture area Aa without changing the receiver collection area Ar.

In comparison with the linear solar energy collector system in FIG. 7, although the spacing between the irradiation areas is doubled, with use of insulated non-irradiation areas, heat radiation from the insulated areas is reduced so that this collector system can heat the heat medium at a higher temperature.

Second Embodiment

FIG. 14A is a top view of a structure model of linear solar energy collector system according to a second embodiment while FIG. 14B is a side view of the same.

The present embodiment is configured that the concentration ratio in the irradiation areas is increased as they are closer to a heat source on the west side. That is, reflected light by the first and second reflective lines L8, L7 from the east side are focused on different irradiation areas, reflected light by the third and fourth reflective lines L6, L5 are focused on the same irradiation area, and reflected light by the fifth to eighth reflective lines L4 to L1 are focused on the same irradiation area.

Thus, the second embodiment can further heighten the temperature of the heat source by setting the concentration ratio of arbitrary positions of the receiver 2 in accordance with a required temperature of the heat source.

Third Embodiment

FIG. 15A is a top view of a structure model of linear solar energy collector system according to a third embodiment while FIG. 15B is a side view of the same.

As in the second embodiment, it is configured that the concentration ratio in the irradiation areas is increased as they are closer to a heat source on the west side. A difference from the second embodiment is in that the concentration ratio is increased not gradually but stepwise.

In FIG. 15B reflected light by the first to fourth reflective lines L8 to L5 from the east side are focused on different irradiation areas, reflected light by the fifth and sixth reflective lines L4 and L3 are focused on the same irradiation area and reflected light by the seventh to eighth reflective lines L2 to L1 are focused on the same irradiation area. The third embodiment can attain the same effects as the second embodiment.

Fourth Embodiment

FIG. 16 is a side view of a structure model of a linear solar energy collector system according to a fourth embodiment.

In the present embodiment the reflective surface of each mirror segment is an east-west curved surface. This is to reduce the receiver concentration area Ar without a decrease in the mirror aperture area Aa to enlarge the concentration ratio X. The cross section of the curved surface can be any curve such as circle, elliptic circle, or parabola. Especially, a cylindrical parabola surface with the heat collecting pipe as a focal line can effectively irradiate the heat collecting pipes with a larger amount of light since it can prevent the reflected light from spreading compared with a plan surface.

Fifth Embodiment

FIGS. 17A to 17C are a top view, a front view, and a side view of a structure model of linear solar energy collector system according to a fifth embodiment, respectively.

FIG. 18 shows the essential structure of a receiver 21.

This linear solar energy collector system comprises a receiver 21 having a compound parabolic concentrator 77 in replace of the receiver 2 in FIGS. 7A to 7C.

In FIG. 18 the cross section or xy coordinates of the surface of the compound parabolic concentrator 77 is expressed by the following equations (6) to (9):

Relative to 0≦θ≦(π/2)+θ₁

x=±a{ sin θ+θ cos(θ−π)}  (6)

y=a{ cos θ+θ sin(θ−π)}  (7)

Relative to (π/2)+θ₁≦θ≦(3π/2)−θ₁

x=±a{ sin θ+p cos(θ−π)}  (8)

y=a{ cos θ+p sin(θ−π)} where p={θ+θ ₁+(π/2)cos(θ−θ₁)}/{1+sin(θ−θ₁)}  (9)

where a is a radius of the heat collecting pipe 6, z axis (not shown) is along the length of the heat collecting pipe 6, a negative side of y axis is towards a vertical point, a central axis coordinate of the heat collecting pipe 6 is x=0, y=0, and θ₁ is the maximum incidence angle of the compound parabolic concentrator 77.

By defining the coordinates x, y as above, it is made possible to reduce the diffusion of the reflected light to a minimum and irradiate the heat collecting pipe 6 with a larger amount of light. The derivation process of the above equations is disclosed in the following documents D1 and D2:

D1: “High Collection Nonimaging Optics”, pp. 263-266, First edition, December 1989, written by W. T. Welford, R. Winston, published by Academic Pr ISBN-10:0127428852 ISBN-13:978-0127428857 D2: “Dyna”, year 77, No. 163, pp. 132-140, Medellin, September 2010, ISSN0012-7353 “MODELING OF DIRECT SOLAR RADIATION IN A COMPOUND PARABOLIC COLLECTOR (CPC) WITH THE RAY TRACKING TECHNIQUE”

The above equations are described in Section 3.1, page 134 of the document D2 and t, θa therein correspond to θ, θ₁ of the above equations.

Sixth Embodiment

FIG. 19 is a front view of a structure model of linear solar energy collector system according to a sixth embodiment.

This linear solar energy collector system comprises the receiver 21 as in the fifth embodiment. A difference from the fifth embodiment is in that the arrangement of the mirror segments is asymmetric as in FIG. 8, and the number of mirror segments on the north side of the light receiving line G is larger than that on the south side.

Also, along with the asymmetric arrangement of the mirror segments, the aperture center of the compound parabolic concentrator 77 is oriented differently from that in the fifth embodiment. That is, it is inclined at an angle θ₂ from the vertical direction in the fifth embodiment. The angle θ₂ is defined by the following equations (10), (11):

${\cos \; 2\theta_{1}} = \frac{{2H^{2}} + \left( {\frac{n}{m + n}L} \right)^{2} + \left( {\frac{n}{m + n}L} \right)^{2} - L^{2}}{2\sqrt{\left\{ {H^{2} + \left( {\frac{m}{m + n}L} \right)^{2}} \right\} \left\{ {H^{2} + \left( {\frac{n}{m + n}L} \right)^{2}} \right\}}}$ $H = {\frac{\frac{m}{m + n}L}{\tan \left( {\theta_{1} - \theta_{2}} \right)} = \frac{\frac{n}{m + n}L}{\tan \left( {{90{^\circ}} - \left( {\theta_{1} + \theta_{2}} \right)} \right)}}$

where m:n is a ratio of the number of the mirror segments placed on the south side and that placed on the north side where m<n.

Thus, it is made possible to maximally increase the amount of incident light on the compound parabolic concentrator 77 and maximally increase the amount of light irradiating the heat collecting pipe 6 on average a year by inclining the angle of the compound parabolic concentrator 77 by θ₂.

The equation (10) is calculated by the law of cosines and Pythagorean theorem, a²=b²+c²−2bccosA. That is, a²=L², b²=H²+{m/(m+n)*L}², c²=H²+{n/(m+n)*L}² and A=2θ₁ are substituted into the equation of the Pythagorean theorem. Further, it is derived from the tangent of two right-angled triangles with respective apex angles of θ₁−θ₂, θ₁+θ₂.

Seventh Embodiment

FIGS. 20A, 20B show an example of a structure model of linear solar energy collector system according to a seventh embodiment.

This linear solar energy collector system is the one according to the first embodiment in FIGS. 13A, 13B having the receiver 21 in FIG. 18 in replace of the receiver 2. The present embodiment can attain the effects of both the first and fifth embodiments.

Eighth Embodiment

FIGS. 21A, 21B show an example of a structure model of linear solar energy collector system according to an eighth embodiment.

This linear solar energy collector system is the one according to the second embodiment in FIGS. 14A, 14B having the receiver 21 in FIG. 18 in replace of the receiver 2. The present embodiment can attain the effects of both the second and fifth embodiments.

Ninth Embodiment

FIGS. 22A, 22B show an example of a structure model of linear solar energy collector system according to a ninth embodiment.

This linear solar energy collector system is the one according to the third embodiment in FIGS. 15A, 15B having the receiver 21 in FIG. 18 in replace of the receiver 2. The present embodiment can attain the effects of both the third and fifth embodiments.

Moreover, the configuration of the linear solar energy collector system according to one embodiment can be modified as follows.

1. The concentration ratio is varied in accordance with a time zone, for example, in the morning and evening during which a large irradiation loss occurs due to cosine low or shadowing, and during culmination in which a small irradiation loss occurs. Thereby, a heat medium at a required temperature can be stably generated for the supply to the heat source. 2. The position of the insulated elements for the non-irradiation area is changed in accordance with the position of the irradiation areas. Thus, even with a change in the non-irradiation areas along with a variation in the concentration ratio, thermal loss can be reduced by moving the insulated elements to a proper position.

Although the present invention has been described in terms of exemplary embodiments, it is not limited thereto. It should be appreciated that variations or modifications may be made in the embodiments described by persons skilled in the art without departing from the scope of the present invention as defined by the following claims. 

1. A linear solar energy collector system, comprising: reflective lines arranged in parallel in a south-north direction; heliostats mounted on the reflective lines, respectively, each comprised of mirror segments to reflect solar radiation; a light receiving line set above the reflective lines in an east-west direction; a receiver mounted on the light receiving line, to receive light reflected from the heliostats and collect heat from the light; and an angular adjuster to adjust angles of the mirror segments individually to irradiate a same light receiving area on the receiver with the reflected light from east-west neighboring reflective lines and thereby adjust a concentration ratio.
 2. A linear solar energy collector system according to claim 1, wherein: the receiver includes a heat collecting pipe filled with a heat medium as a fluid; and the heat collecting pipe is segmented into an irradiation area irradiated with the reflected light from the mirror segments and a non-irradiation area arranged at both ends of the irradiation area.
 3. A linear solar energy collector system according to claim 2, wherein the irradiation area is configured to transfer heat to the non-irradiation area when heated with the reflected light and cause a heat transfer in the fluid inside the heat collecting pipe.
 4. A linear solar energy collector system according to claim 1, wherein the angular adjuster is configured to adjust south-north and east-west rotation angles of the mirror segments.
 5. A linear solar energy collector system according to claim 1, wherein the mirror segments each include a curved reflective surface.
 6. A linear solar energy collector system according to claim 4, wherein the angular adjuster is configured to adjust the east-west rotation angles commonly and adjust the south-north rotation angles individually.
 7. A linear solar energy collector system according to claim 1, wherein each of the mirror segments is a standard module having a south-north length twice as long as an east-west length; and two groups of mirror segments arranged in tandem are disposed to face each other on the reflective lines, placing the light receiving line in-between.
 8. A linear solar energy collector system according to claim 1, wherein a south-north spacing of the mirror segments is set to reduce an optical loss between south-north neighboring mirror segments due to blocking or shadowing, such that the further from the light receiving line the mirror segments are, the wider the spacing is.
 9. A linear solar energy collector system according to claim 1, wherein: when the linear solar energy collector system is installed in the northern hemisphere, a north-side length of the reflective lines from the light receiving line is set to be longer than a south-side length; and when the linear solar energy collector system is installed in the southern hemisphere, the south-side length of the reflective lines from the light receiving line is set to be longer than the north-side length.
 10. A linear solar energy collector system according to claim 1, wherein: the receiver includes a heat collecting pipe filled with a heat medium, arranged above all the heliostats, and connected at one end to a heat source; and the heat collecting pipe is configured to receive the reflected light from the heliostats and collect heat from a heated heat medium.
 11. A linear solar energy collector system according to claim 1, wherein: the receiver includes heat collecting pipes arranged in parallel, is covered with a thermal insulated wall above the heat collecting pipes, and includes an endothermic net below the heat collecting pipes, having a cavity window function; the thermal insulated wall is a cover with an arc-like cross section to enclose the heat collecting pipes and has both ends projecting downward from edges of the endothermic net; and the endothermic net is a stainless mesh with a well curb or a honey comb structure of a certain thickness, to allow the reflected light from the heliostats to transmit through the mesh to inside but not to allow an irradiation of the reflected light to travel outside from the mesh.
 12. A linear solar energy collector system according to claim 1, wherein the receiver includes a compound parabolic concentrator to reflect the reflected light from the mirror segments to the heat collecting pipe.
 13. A solar power generator system, comprising: a backup heater using the linear solar energy collector system according to the claim 1 to heat the fluid up to a first temperature lower than an intended temperature; and a main heater using another type solar energy collector system more suitable for high-temperature energy concentration than the linear solar energy collector system, to increase the temperature of the fluid up to a second temperature as the intended temperature. 